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>>A number of advanced coelurosaurs had more or less dromaeosaur-like claws
(_Rahonavis_, _Megaraptor_, rudimentary in _Archaeopteryx_), and there are
significant differences in the foot claws of troodonts and dromaeosaurs.
Troodont pelves have a forward- or downward-pointing pubis, unlike birds,
dromaeosaurs, and ornithischians. But I concede that they don't look a whole
lot like tyrannosaurs or ornithomimosaurs, either.<<
They do, however, look a lot like _baby_ tyrannosaurids (especialy the
ornithomimes). Imagine a primitive small predator (probably a lot like
compsognathus) which, at the end of the Jurassic, diversified into three kinds.
One, was a heron-like runner, the other, a predator of small animals that used
hands, the third was a predator of large animals that used its mouth and not its
hands. All of the superficial adaptations of the three groups, the long necks
the ornithomimes, the sickle-claws of the troodonts, and the two fingers of the
tyrannosaurs, are all reflections of those three lifestyles.